In this paper, we propose an additional noise-free, independent center frequency and bandwidth tunable optical filter based on stimulated Brillouin scattering (SBS) losses. By suppressing the out-of-band signal with two broadened symmetric SBS losses, tunable pass bandwidths from 500 MHz to 9.5 GHz and the independent center frequency tunability are demonstrated. Considering the limited SBS interaction in the center frequency range, a flat-top response with minimum 0.3 dB ripple is achieved. Assisted by the extra suppression from polarization pulling, a maximum selectivity of 20 dB and an ultrahigh $250\mathrm{dB}/\mathrm{GHz}$ roll-off are reached. A gain-based SBS filter adds noise to the filtered signal. However, for our proposed filter setup, no additional noise is detected due to the transparency in the passband. Considering the wide independent bandwidth and center frequency tunability, flat-top response, and low-noise characteristic, our proposed filter can be perfectly used as a supplement of most commercialized conventional tunable optical single bandpass filters, whose minimum bandwidth is limited by 10 GHz.

The distributed Brillouin sensing technique has been developed rapidly since its first demonstration three decades ago. Numerous investigations on the performance enhancement of Brillouin sensors in respect to spatial resolution, sensing range, and measurement time have paved the way to its industrial and commercial applications. This chapter provides an overview of different Brillouin sensing techniques and mainly focuses on the most widely used one, the Brillouin optical time domain analysis (BOTDA). The history and the development of Brillouin sensing regarding the performance enhancement in various methods and their records will be reviewed, commented, and compared with each other. As well, related sensing errors and limitations will be discussed, together with the corresponding strategies to avoid them.

We report on two previously unknown non-local effects that have been found to impair Brillouin optical time-domain analysis (BOTDA) sensors that deploy limited extinction ratio (ER) pump pulses. The first one originates in the increased depletion of the pedestal of the pump pulses by the amplified probe wave, which in turn entails a reduced amplification of the probe and a measurement distortion. The second effect is due to the interplay between the transient response of the erbium-doped fiber amplifiers (EDFA) that are normally deployed to amplify the pump and the pedestal of the pump pulses. The EDFA amplification modifies the pedestal that follows the pulses in such a way that it also leads to a distortion of the measured gain spectra after normalization. Both effects are shown to lead to non-local effects in the measurements that have similar characteristics to those induced by pump pulse depletion. In fact, the total depletion factor for calculations of the Brillouin frequency shift (BFS) error in BOTDA sensors is shown to be the addition of the depletion factors linked to the pump pulse as well as the pedestal. A theoretical model is developed to analyze both effects by numerical simulation. Furthermore, the effects are investigated experimentally in long-range BOTDA sensors. The pedestal depletion effect is shown to severely constrain the probe power as well as the minimum ER of the pulses that can be deployed in BOTDA sensors. For instance, it is shown that, in a long-range dual-probe BOTDA, an ER higher that 32-dB, which is above that provided by standard electro-optic modulators (EOM), is necessary to be able to deploy a probe power of −3 dBm, which is the theoretical limit for that type of sensors. Even more severe can be the limitation due to the depletion effect induced by the EDFA transient response. It is found that the impairments brought by this effect are independent of the probe power, hence setting an ultimate limit for the BOTDA sensor performance. Experimentally, a long-range BOTDA deploying a 26-dB ER EOM and a conventional EDFA is shown to exhibit a BFS error higher than 1 MHz even for very small probe power.

In this paper, a novel method for Brillouin optical time-domain analyzers exploiting the gain spectrum engineering will be proposed for the first time, to the best of our knowledge. By superimposing the Brillouin gain with two symmetric loss spectra, new degrees of freedom will be provided to engineer the spectrum of the Brillouin interaction. This leads to a Brillouin gain shape which is much more robust to noise influences than the conventional one. Simulations and experiment are in very good agreement to each other and demonstrate a more than 3-dB measurement accuracy enhancement. Since for the proposed method the frequency error is less susceptible to the fiber loss, the sensing range can be extended by up to 60%. This paper might open a new way to enhance and adapt the distributed Brillouin sensing performances by an engineering of the spectrum shape.

An all-fiber 1.3-μm femtosecond pulse source has been demonstrated via Cherenkov radiation in highly nonlinear fiber seeded by an ultrafast Er-doped fiber laser. Through the dispersion management in total process, the generated pulses can be as short as 29 fs. This pulse source has a 15% conversion efficiency accounting for the input power and the single pulse energy reaches 76 pJ. Furthermore, a simulation has been carried out to illustrate the pulse evolution on the spectral and temporal progress in fibers. To the best of our knowledge, this is the first report of all-fiber 1.3 μm ultrashort pulse source with the duration below 30 fs.

In this paper, the detrimental effects due to the inevitable dispersion of single-mode fibers for stimulated Brillouin scattering (SBS) based microwave photonic notch filters (MPNF) with sideband amplitude and phase control are investigated. With an inappropriate dispersion compensation, the experimental demonstration shows a notch center frequency shift of 8.3 MHz in maximum and a stopband rejection reduction by 21 dB for the MPNF. The simulation and experiment are in good agreement. Furthermore, the criteria of optimizing the filter performance are also discussed both theoretically and experimentally. These results can help design MPNF based on SBS and benefit other microwave photonic applications, which rely on the phase difference of optical waves.